The present invention relates to a brush seal device for sealing a gap between two parts that move relative to each other about a rotating shaft of an airplane, gas turbine or the like. More particularly, the present invention relates to the field of a brush seal device for sealing a gap between two parts by causing a brush seal to elastically deform according to movement of one part even when the dimension of the gap is changed and thus preventing contact wear.
There is a brush seal device 100 of FIG. 13 as an example of the related art of the present invention.
FIG. 13 is a cross-sectional view of the brush seal device 100. The brush seal device 100 is mounted between a rotating shaft 120 and a hole formed in a casing 110, and the rotating shaft 120 extends through the hole. This casing 110 is a part of a steam turbine. The brush seal device 100 separates the gap between the casing 110 and the rotating shaft 120 so as to seal a sealed fluid (steam fluid) flowing in the gap.
The brush seal device 100 has a ring shape, and is mounted in an annular groove 112 in the casing 110. The brush seal device 100 mainly includes a brush seal 109, a back plate 102 and a retaining plate 103. The brush seal 109 is formed from bristles 101 radially arranged into a wall shape along the circumference. The bristles 101 are connected together at one end to form an attachment portion 104. A free end face 105 of the brush seal 109 faces the rotating shaft 120. The bristle 101 of the brush seal 109 commonly has a diameter of 0.25 mm or more.
The annular back plate 102 has its side surface 108 in contact with one side surface of the brush seal 109. The annular back plate 102 supports the bristles 101 against the pressure of the sealed fluid.
The retention plate 103 has a ring shape, and is mounted on the other side surface of the brush seal 109. The attachment portion 104 of the brush seal 109 is thus held between the retaining plate 103 and the back plate 102. The retention plate 103 has a small width in the radial direction of the brush seal 109 so that the brush seal 109 is exposed to the sealed fluid.
The back plate 102, the attachment portion 104 of the brush seal 109 and the retaining plate 103 are welded together to form a connected portion 106.
FIG. 14 is a front view of the brush seal 109, illustrating the present invention or the related art. The brush seal device 100 of FIG. 14 is in a normally fitted state in which the brush seal 109 and the rotating shaft 120 do not move relative to each other. In this normal state, the rotating shaft 120 shown by the virtual line in FIG. 13 is located in contact with or near the free end face of the brush seal 109.
Although not shown in the figure, a brush seal device according to another example of the related art has a small gap between the side surface 108 of the back plate 102 and the side surface of the brush seal 101. However, the bristle 101 having a diameter of 0.25 mm or more hinders the function of the gap. In other words, the bristles 101 will not be deflected according to movement of the rotating shaft 120. This accelerates wear of the free end face 105 of the bristles 101. Moreover, such a large diameter of the bristle 101 makes it impossible to form a thicker wall of the bristles in view of the friction with the rotating shaft. This results in degraded sealing capability.
In the above brush seal device 100, when the rotating shaft 120 contacts the brush seal 109 due to vibration or the like as shown in FIG. 13, the brush seal 109 is further tilted in the rotation direction under the pressure from the rotating shaft 120 as shown in FIG. 15.
If the sealed fluid has a high pressure P1 in this state, the brush seal 109 is pressed against the side surface 108 of the back plate 102 due to a large difference between the high and low pressures P1 and P2 (P1xe2x88x92P2), as shown in FIG. 16.
In the state of FIG. 16, the bristles 101 of the brush seal 109 are less likely to be deflected because they are pressed against the side surface 108 of the back plate 102. In other words, the bristles 101 are less likely to be deflected according to movement of the rotating shaft 120. Moreover, the sealed fluid enters between the bristles 101, whereby one bristle 101 is raised relative to the other. As a result, the tilted bristles 101 try to reduce the tilting angle of the raised bristles 101. Since the raised bristles 101 have a long radial length, the pressure from the rotation shaft 120 is increased, causing wear of the brush seal 2.
When the vibration of the rotating shaft 120 is reduced as shown in FIG. 17, the gap C between the worn free end face 105 of the bristles 101 and the rotating shaft 120 is increased as shown in FIG. 18. As a result, the sealed fluid leaks through the gap C. Moreover, when the pressure P1 of the sealed fluid is reduced (i.e., when the difference between the pressure P1 and the pressure P2 in the downstream region (P1xe2x88x92P2) is reduced), the rotation force of the rotating shaft 120 becomes dominant. Accordingly, the gap C between the rotating shaft 120 and the free end face 105 of the bristles 101 may be increased due to the rotation force. In this case as well, the sealed fluid leaks through the gap C.
The preset invention is made in view of the above problems. It is an object of the present invention to improve flexibility of a brush seal against the pressure of a rotating shaft, and reduce the wear due to friction between the brush seal and the rotating shaft by the flexibility of the brush seal.
It is another object of the present invention to improve sealing capability by improving the ability of the brush seal to deflect according to movement of the rotating shaft.
It is still another object of the present invention to improve sealing capability by densely arranging bristles of a smaller diameter into a wall shape.
It is yet another object of the present invention to improve sealing capability and prevent friction-induced damages by preventing abnormal movement of the aligned bristles.
It is a further object of the present invention to enable the brush seal to be deformed according to the pressure value of a sealed fluid by controlling in balance the front pressure of the sealed fluid acting on the bristles and the back pressure of the sealed fluid in a recess passing through the brush seal.
The present invention is made to solve the above problems. Means for solving the problems are structured as follows:
A brush seal device according to the present invention is mounted to one of two parts that move relative to each other with a gap therebetween, and seals the gap between the parts by a brush seal. The bush seal device includes: a brush seal formed from bristles arranged into a wall shape, and including an attachment portion formed by connecting the bristles together at one end, and a free end face facing an opposing surface of the other part; a back plate connected to the attachment portion of the brush seal, and including a support surface for supporting a side surface of the brush seal; and a retaining plate for retaining the attachment portion of the brush seal between the retaining plate and the back plate. The support surface of the back plate and an opposing surface of the brush seal are disposed at a distance from each other. The bristle of the brush seal has a diameter of 0.15 mm to 0.008 mm.
In the brush seal device of the present invention, the bristles are disposed at a distance from the support surface of the back plate, and the bristle has a diameter of 0.15 mm to 0.008 mm. Therefore, even when the other part contacts the free end face of the bristles, the bristles can be elastically deformed toward the support surface. For example, even if the bristles abut on the rotor, they are moved while reducing the contact pressure. Accordingly, wear of the bristles is prevented.
Moreover, since the bristles are thin, they can be densely arranged into a wall, allowing improvement in sealing capability.